为什么我得到“运行异常”错误？

Question

我由图像阵列与较少数量的图像视图来设置。我想要10个图像随机分配给4个图像视图，然后通过网格显示。每次运行代码时，我都会遇到一个错误，“运行应用程序时出现异常”。这是图像的路径吗？我没有看到任何明显的错误。

package Flag; 
import java.util.Random; 
import javafx.application.Application; 
import javafx.geometry.Pos; 
import javafx.scene.Scene; 
import javafx.scene.image.Image; 
import javafx.scene.image.ImageView; 
import javafx.scene.layout.GridPane; 
import javafx.stage.Stage; 

public class Flag extends Application { 

    @Override public void start(Stage primaryStage) { 
     // Initialize Variables 
     GridPane pane = new GridPane(); 
     pane.setAlignment(Pos.CENTER); 
     ImageView [] imv = new ImageView [4]; 
     Image [] images = new Image[10]; 

     //Fill Images array 
     images[0] = new Image(Flag.class.getResourceAsStream("images/flag0.gif")); 
     images[1] = new Image(Flag.class.getResourceAsStream("images/flag1.gif"));  
     images[2] = new Image(Flag.class.getResourceAsStream("images/flag2.gif")); 
     images[3] = new Image(Flag.class.getResourceAsStream("images/flag3.gif")); 
     images[4] = new Image(Flag.class.getResourceAsStream("images/flag4.gif")); 
     images[5] = new Image(Flags.class.getResourceAsStream("images/flag5.gif"));  
     images[6] = new Image(Flag.class.getResourceAsStream("images/flag6.gif")); 
     images[7] = new Image(Flag.class.getResourceAsStream("images/flag7.gif")); 
     images[8] = new Image(Flags.class.getResourceAsStream("images/flag8.gif")); 
     images[9] = new Image(Flags.class.getResourceAsStream("images/flag9.gif")); 

      //Random number 
     Random rand = new Random(); 

     //Give Each Image an Image View 
     for (ImageView imv1 : imv) { 
/*This is line 38*/ imv1.setImage(images[rand.nextInt(9)]); 
     } 

     // Add nodes to pane 
     pane.add(imv[0], 0, 0); 
     pane.add(imv[1], 0, 1); 
     pane.add(imv[2], 1, 0); 
     pane.add(imv[3], 1, 1); 

    //Create a scene and place it in the stage 
     Scene scene = new Scene(pane); 
     primaryStage.setTitle("ShowGridPane"); 
     primaryStage.setScene(scene); 
     primaryStage.show(); 
    } 

    public static void main(String[] args) { 
     Application.launch(args); 
    } 
} 

这里的日志

Exception in Application start method 
java.lang.reflect.InvocationTargetException 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
    at java.lang.reflect.Method.invoke(Method.java:606) 
    at com.javafx.main.Main.launchApp(Main.java:642) 
    at com.javafx.main.Main.main(Main.java:805) 
Caused by: java.lang.RuntimeException: Exception in Application start method 
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:403) 
    at com.sun.javafx.application.LauncherImpl.access$000(LauncherImpl.java:47) 
    at com.sun.javafx.application.LauncherImpl$1.run(LauncherImpl.java:115) 
    at java.lang.Thread.run(Thread.java:724) 
Caused by: java.lang.NullPointerException 
    at Flag.Flag.start(FlagsHwB.java:38) 
    at com.sun.javafx.application.LauncherImpl$5.run(LauncherImpl.java:319) 
    at com.sun.javafx.application.PlatformImpl$5.run(PlatformImpl.java:215) 
    at com.sun.javafx.application.PlatformImpl$4$1.run(PlatformImpl.java:179) 
    at com.sun.javafx.application.PlatformImpl$4$1.run(PlatformImpl.java:176) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at com.sun.javafx.application.PlatformImpl$4.run(PlatformImpl.java:176) 
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method) 
    at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29) 
    at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:73) 
    ... 1 more 
Java Result: 1 

Answer 1

images[9] - 这不存在。该数组只有九个元素。该错误消息说，这：Caused by: java.lang.ArrayIndexOutOfBoundsException: 9

Answer 2

问题是因为

Image [] images = new Image[9]; 

要初始化9个元素的数组，并试图插入10个元素融入到它的。

images[9] = new Image(Flags.class.getResourceAsStream("images/flag9.gif")); 

代表9th index和10th element。只是增加数组大小来10即

Image [] images = new Image[10]; 

一个更好的选择是，如果你不知道该数组的大小使用一个ArrayList。 ArrayList调整自己的元素添加。

编辑 - 为每个用户评论

的NullPointerException是因为你没有初始化任何你的ImageView。在使用ImageView之前初始化它们。

for (ImageView imv1 : imv) { 
    imv1 = new ImageView(); // Initialization 
    imv1.setImage(images[rand.nextInt(9)]); 
} 

，或者你可以直接使用

for (ImageView imv1 : imv) { 
    imv1 = new ImageView(images[rand.nextInt(9)])); 
}